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Digestive System – Part 1
Function of the Digestive System
To convert foods into
simpler molecules
that can be absorbed
and used by the cells
of the body
Parts of the Digestive System
• The digestive system
includes the mouth, pharynx,
esophagus, stomach, small
intestines and large
intestines
• Salivary glands, pancreas,
gall bladder and liver add
secretions to the digestive
system
Mouth
Digestion begins at the
mouth
Teeth tear and crush
food into smaller pieces.
Mechanical Digestion
(Chewing)
Mechanical digestion
is the physical
breakdown of large
pieces of foods into
smaller pieces
Teeth
Teeth do most of the
mechanical digestion
by cutting, tearing, and
crushing food into
small fragments
Teeth are anchored in
the bones of the jaw
Chemical Digestion
As you chew your
food, digestive
enzymes begin the
breakdown of food
into smaller molecules
Saliva
As you chew, the salivary
glands secrete saliva
Saliva moistens food
Contains the enzyme
Amylase that breaks
starches into smaller
sugars
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Digestive System – Part 2
Esophagus
The tube that connects
the mouth to the stomach
Peristalsis
Peristalsis - food is moved
along the esophagus by
contractions of smooth
muscle
Stomach
Food from the
esophagus empties
into a large muscular
sac called the stomach
The stomach continues
the mechanical and
chemical digestion of
food
Chyme
Chyme – semifluid, partially digested food that
is expelled from the stomach to the duodenum
Duodenum
Duodenum
The chyme enters the
duodenum, the first part
of the small intestine.
The duodenum is where
all of the digestive
enzymes enter
Jejunum
Jejunum – second part of the small intestine
Most of the nutrients in food are absorbed here
Villi and Microvilli
Villi and microvilli - the folded surface of the
small intestine. Nutrient absorption occurs here
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Digestive System – Part 3
ileum
Ileum – third part of the small intestine
Vitamin B12 and bile salts are absorbed here
Large Intestine (colon)
Water, cellulose and other undigested material
enter the large intestine
Primary function of the large intestine is to
remove water from the undigested material
Rectum
Final section of the large
intestine
Temporary storage for
feces
Pancreas
Pancreas – the gland that controls blood
sugar levels
Produces insulin and glucagon. Secretes
digestive enzymes that break down food.
Liver
The liver produces bile, which acts like a detergent,
dissolving and dispersing droplets of fat.
Breaks down and detoxifies substances in the body
Gall Bladder
Stores bile produced by the liver and secretes it
to the small intestine.
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Large Intestine (colon)
The material that leaves the
small intestine is nutrient free
Water, cellulose and other
undigestible material enter the
large intestine
Primary function of the large
intestine is to remove water
from the undigested material
The waste material that
remains passes through the
rectum and is eliminated from
the body at the anus
Bacteria in the large
intestine produces
vitamin K
Accessory Structures of Digestion
The pancreas produces
enzymes that break down
carbohydrates, proteins, lipids
and nucleic acids.
Gallbladder
Liver
The pancreas also produces
sodium bicarbonate, a base
that neutralizes stomach acid.
The liver produces bile, which
acts like a detergent, dissolving
and dispersing droplets of fat.
Bile is stored in the gallbladder.
Duodenum
Pancreas
ileum
The duodenum is much shorter
than the remaining parts of the
small intestine - the jejunum
and ileum
Much of the chemical digestion
has been completed when the
chyme reaches the jejunum
The chyme is now a rich
mixture of medium and small
nutrient molecules
Chemical & Mechanical
Digestion in Stomach
Chemical digestion - HCl and Pepsin begins the process of
protein digestion.
Mechanical digestion - Stomach muscles contract to churn
and mix stomach fluids and food producing Chyme.